JP2012250620A - Pneumatic tire for off-road - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire for off-road which maintains traction performance on an uneven road surface and besides, achieves improved driving stability on a hard road surface.SOLUTION: The pneumatic tire for off-road includes: a bead apex rubber which passes through a main part and a folded part of a carcass from a bead core and extends radially outwardly in a tapered form; and a bead flipper which comprises rubber coated textile of organic fiber and has a U shape formed by folding a flipper inside part and a flipper outside part at both tire axial-direction ends of a flipper bottom part in contact with a radial-direction inner face of the bead core, wherein the flipper inside part comes in contact with a tire axial-direction inner side face of the bead apex rubber and ends on the inner side face, and wherein the flipper outside part comes in contact with a tire axial-direction outer side face of the bead apex rubber and ends on the outer side face. A tire axial-direction core width of the bead core is 8 to 10 mm, and a tire axial-direction bead base width from a tire axial-direction outer side face of the bead part to a distal end of a bead toe part is 18 to 20 mm. Aramid fiber is used as the organic fiber of the bead flipper.

Description

  The present invention relates to an off-road pneumatic tire that is particularly suitable for a rally and can improve steering stability on a hard road surface while maintaining traction on an uneven road surface.

  In off-road tires used for competitions such as rally and dirt trials, when driving on hard roads, if tire deformation during cornering increases, steering stability decreases and lap time decreases. For this reason, conventionally, the bead apex rubber is made higher or the carcass turn-up portion is made higher to increase the tire sidewall rigidity, thereby reducing tire deformation during cornering.

  However, in such a tire, the longitudinal spring constant of the tire increases as the sidewall rigidity increases. For this reason, if the sidewall rigidity is increased too much, there is a problem that when the vehicle runs on an uneven road surface, the jumping of the tire becomes large, the road surface following ability is deteriorated, and the traction property is lowered. Thus, the traction on the uneven road surface and the steering stability on the hard road surface are in a trade-off relationship, and it is difficult to achieve both at a high level.

  On the other hand, in the dirt course for competitions, ridges are deeply formed. Therefore, when the tire collides with this rudder with a rudder angle, the bead portion may be strongly twisted to cause rim disengagement. Therefore, in off-road tires, it is desirable to reduce the inner diameter of the bead core and increase the fitting force with the rim compared to normal on-road tires, but in this case, the rim assembly performance is greatly improved. There is a problem that it falls.

  As shown in FIG. 4, conventionally, a bead core b is wrapped around a bead core b together with a bead apex rubber c in a U shape using a bead flipper a made of a rubberized woven fabric of nylon fiber, for example, as shown in FIG. Prevention of peeling of the bead core b and the bead apex rubber c at the time of tire formation is performed (see, for example, FIGS. 6A and 6B of Patent Document 1).

JP 2000-247119 A

  Therefore, the present invention uses an aramid fiber for the bead flipper and, based on the fact that the core width of the bead core and the bead base width of the bead part are wider than before, the bead deformation is suppressed while suppressing an increase in the longitudinal spring constant. An object of the present invention is to provide an off-road pneumatic tire that can be suppressed, can improve steering stability on a hard road surface while maintaining traction on an uneven road surface, and can improve rim detachment resistance.

In order to solve the above-mentioned problem, the invention of claim 1 of the present application is directed to a main body part extending from the tread part through the sidewall part to the bead core of the bead part, and the circumference of the bead core from both ends of the main body part on the inner side in the tire axial direction. A carcass comprising two or more carcass plies,
A bead apex rubber that extends from the bead core to the outside in the radial direction through the space between the body portion and the folded portion;
And at both ends in the tire axial direction of the bottom of the flipper that is in contact with the inner surface in the radial direction of the bead core, the inner portion of the flipper that is cut off in contact with the inner side surface in the tire axial direction of the bead apex rubber, and the outer side in the tire axial direction of the bead apex rubber is cut off. A bead flipper made of a rubberized woven fabric of organic fibers and a U-shaped bent outer side of the flipper,
A core width in the tire axial direction of the bead core is 8 to 10 mm,
And the bead base width in the tire axial direction from the tire axial direction outer side surface of the bead portion to the tip of the bead toe portion is 18 to 20 mm,
In addition, an aramid fiber is used as the organic fiber of the bead flipper.

  According to a second aspect of the present invention, the bead portion is provided between the carcass and the bead flipper, on the base portion along the flipper bottom portion, on the rising portion along the flipper inner portion, and on the flipper outer portion. It is characterized by having a U-shaped configuration consisting of an outer rising portion along the core, and a core surrounding rubber layer made of hard rubber having a thickness of 0.2 to 1.0 mm and a rubber hardness of 70 to 80 °. Yes.

  According to a third aspect of the present invention, the bead portion includes a chafer bottom piece portion forming a radially inner surface of the bead portion, a chafer inner piece portion forming an inner surface of the bead portion, and a chafer outer piece portion forming an outer surface of the bead portion. A U-shaped sheet-shaped chafer for preventing rim displacement, a bottom portion extending along the chafer bottom piece between the chafer and the carcass, and along the chafer inner piece It is characterized in that a toe reinforcing rubber made of a hard rubber having a rubber hardness of 70 to 80 ° having at least an L-shaped main portion that joins the extending inner portion is provided.

  According to a fourth aspect of the present invention, the carcass is composed of three carcass plies.

  In this specification, unless otherwise specified, the dimensions and the like of each part of the tire are values specified when the bead part is held in accordance with the rim width defined by the tire size in a non-rim assembled state. .

  The rubber hardness is a durometer A hardness measured in a 23 ° C. environment using a durometer type A based on JIS-K6253.

  When tension is applied to the carcass cord, a rotational moment around the bead core center point acts on the bead portion. However, in the present invention, the core width of the bead core is set in a range of 8 to 10 mm, which is wider than the conventional one. Therefore, it is possible to increase the resistance against the so-called bead rotation deformation in which the bead portion is inclined in the direction in which the bead toe is lifted due to the rotational moment. Moreover, since the bead base width of the bead portion is 18 to 20 mm, which is wider than the conventional one, the resistance against the bead rotation deformation can be further increased.

  Moreover, aramid fibers are used for the bead flipper. Therefore, since the bead core and the bead apex rubber are more firmly integrated, the bead apex rubber becomes a large resistance and can increase the resistance against the bead rotation deformation, thereby suppressing the bead rotation deformation.

  As a result, the lateral rigidity of the bead portion is increased, and during cornering on a hard road surface, tire deformation that falls from the bead portion to the sidewall portion toward the outer side in the tire axial direction can be suppressed, and steering stability can be improved. In addition, since the increase in the vertical spring constant of the tire is suppressed to a low level, road surface followability with respect to an uneven road surface can be ensured, and the traction property can be maintained at a high level.

  Further, the seat width with the rim is enhanced by the wide width of the core and the bead base and the suppression of the bead rotation deformation. Therefore, it is possible to improve the anti-rim removal performance without increasing the fitting pressure with the rim, that is, without impairing the rim assembly performance.

It is sectional drawing which shows one Example of the pneumatic tire for off-road of this invention. It is an expanded sectional view of a bead part showing bead apex rubber and a bead flipper. It is an expanded sectional view of the bead part which shows a toe reinforcement rubber and a chafer. It is a perspective view which shows the bead flipper of the conventional tire.

Hereinafter, embodiments of the present invention will be described in detail.
In FIG. 1, a pneumatic tire 1 for off-road according to the present embodiment includes a main body 6A that extends from a tread portion 2 through a sidewall portion 3 to a bead core 5 of a bead portion 4, and the both ends of the main body portion 6A. A carcass 6 having a turning portion 6B that is turned around from the inner side in the tire axial direction to the outer side of the bead core 5 and a belt layer 7 arranged on the outer side in the radial direction of the carcass 6 and inside the tread portion 2 are provided.

  The tread portion 2 is formed with a block pattern in which a block B partitioned by a tread groove G having a groove depth of 9.0 mm or more is spaced apart. Similar to the tire, the range of 40 to 65% is preferable. As is well known, the land ratio is indicated by the ratio of the surface area of the block B to the entire tread surface.

  The carcass 6 is formed of at least two carcass plies including a first carcass ply 6a disposed on the tire lumen side and a second carcass ply 6b placed on the outside thereof. In this example, the carcass 6 has a so-called 2-0 structure composed of two carcass plies 6a and 6b. Each of the carcass plies 6a and 6b includes a carcass cord arranged at an angle of, for example, 75 to 90 ° with respect to the tire equator plane Co. As the carcass cord, an organic fiber cord such as polyester, nylon, or rayon is suitably employed. The

  The height of the folded portion 6B of the carcass plies 6a, 6b is not particularly limited, and the same range as the conventional one can be suitably employed. In this example, each folded-back portion 6B is within a region between the carcass maximum width position Pm where the main body portion 6A of the carcass 6 projects most outward in the tire axial direction and the outer end portion in the tire axial direction of the belt layer 7. The case of termination is indicated.

  Each bead portion 4 is provided with a bead apex rubber 8 that tapers radially outward from the bead core 5, and the bead core 5 and the bead apex rubber 8 are integrally wrapped by a U-shaped bead flipper 10. It is. In addition, as the bead core 5, the thing of the well-known structure of cross-sectional substantially rectangular shape which wound the bead wire which consists of hard steel wires etc. in the multi-row multistage, for example is used.

  The bead apex rubber 8 is made of hard rubber having a rubber hardness of 70 to 90 °, and extends from the bead core 5 between the main body portion 6A and the folded portion 6B in a tapered manner outward in the radial direction. The height of the bead apex rubber 8 is not particularly restricted, and a range similar to the conventional one can be suitably employed. In this example, the case where the radial height H1 from the bead base line BL at the outer end of the bead apex rubber 8 is in the range of 25 to 45% of the tire cross-section height HT is shown.

  As shown in FIG. 2, the bead flipper 10 extends from both ends of the flipper bottom 10a in contact with the inner surface in the radial direction of the bead core 5 in the tire axial direction and to the inner surface in the tire axial direction of the bead apex rubber 8. The bead core 5 has a U-shaped cross section in which a flipper inner portion 10i that is interrupted on the inner surface and a flipper outer portion 10o that is in contact with the outer surface in the tire axial direction of the bead apex rubber 8 and that is interrupted on the outer surface are bent. And bead apex rubber 8 are wrapped in a U shape and integrated.

  The bead flipper 10 is formed from a rubberized fabric of organic fibers. As this rubberized woven fabric, a so-called bamboo woven fabric formed by wrapping a thin weft into a plurality of parallel warps separated by a predetermined distance in the longitudinal direction and coated with a coating rubber, or a large number of parallel warps It is possible to use a so-called canvas cloth formed by alternately weaving a plurality of wefts and a so-called canvas cloth covered with a coating rubber. The angle of the warp with respect to the tire circumferential direction is generally in the range of 20 to 70 °. The bead flipper 10 is different from the conventional bead flipper in that an aramid fiber is used as the organic fiber. Specifically, when the woven fabric is a braided woven fabric, at least the aramid fiber is used for the warp. Cords are used, and in the case of canvas fabric, aramid fiber cords are used for both warp and weft. The thickness of the aramid fiber cord is preferably 1600 to 1700 dtex.

  Further, in this example, a core peripheral rubber layer 11 made of hard rubber having a thickness t11 of 0.2 to 1.0 mm and a rubber hardness of 70 to 80 ° is disposed between the carcass 6 and the bead flipper 10. . The core surrounding rubber layer 11 includes a base portion 11a along the flipper bottom portion 10a, an inner rising portion 11i along the flipper inner portion 10i, and an outer rising portion 11o along the flipper outer portion 10o. It is U-shaped.

  In the core surrounding rubber layer 11 of the present example, the outer rising portion 11o is interrupted radially outward from the radially outer surface of the bead core 5 and radially inward from the outer end of the flipper outer portion 10o. The inner rising portion 11i is interrupted radially outside the radially outer surface of the bead core 5 and radially inner than the outer end of the flipper inner portion 10i. In particular, in this example, the inner rising portion 11i is interrupted radially outward from the outer end of the outer rising portion 11o, and further radially outward from the outer end of the flipper outer portion 10o. The case where is reduced is shown.

  Further, as shown in FIG. 3, the bead portion 4 is provided with a sheet-shaped chafer 12 for preventing rim displacement similar to that of the conventional tire. The chafer 12 includes a chafer bottom piece 12 a that forms the inner surface in the radial direction of the bead portion 4, a chafer inner piece portion 12 i that forms the inner surface of the bead portion 4, and a chafer outer piece portion 12 o that forms the outer surface of the bead portion 4. A U-shape. In this example, the case where the chafer 12 is formed from a rubber sheet having excellent wear resistance is shown. However, like the bead flipper 10, the chafer 12 may be formed from a rubberized fabric of organic fibers.

  Further, in the present embodiment, a toe reinforcing rubber 14 made of hard rubber having a rubber hardness of 70 to 80 ° is disposed on the bead portion 4 between the chafer 12 and the carcass 6. The toe reinforcing rubber 14 includes at least an L-shaped main portion 13 that connects a bottom portion 13a extending along the chafer bottom piece portion 12a and an inner portion 13b extending along the chafer inner piece portion 12i. In this example, the case where the toe reinforcing rubber 14 further raises the outer portion 14o extending along the chafer outer piece portion 12o is shown. The toe reinforcing rubber 14 reinforces the bead toe portion 4T by the L-shaped main portion 13 and suppresses deformation of the bead toe portion 4T.

  The toe reinforcing rubber 14 is thick at the intersection P where the bottom portion 13a and the inner portion 13b intersect, and is formed with a thickness t14 of 0.2 to 1.0 mm outside this intersection P. . The thickness ta of the toe reinforcing rubber 14 on the bisector X of the angle of the tip of the bead toe portion 4T is 70% of the distance tb from the tip of the bead toe portion 4T to the carcass 6 on the bisector X. Hereinafter, 60% or less is preferable, and if it exceeds 70%, the bead toe portion 4T becomes too hard, and the rim assembly performance is deteriorated and the bead toe portion 4T tends to be easily damaged. In the bead toe portion 4T, the rubber 15 interposed between the toe reinforcing rubber 14 and the carcass 6 is made of rubber having the same hardness (rubber hardness of 55 to 75 °) as that of the conventional rubber disposed in the bead toe portion. The

  In the tire 1 of the present embodiment, the core width W5 in the tire axial direction of the bead core 5 is set in a range of 8 to 10 mm and wider than the core width W5 of the conventional off-road tire, and the bead portion 4 The bead base width W4 in the tire axial direction from the outer surface in the tire axial direction to the tip of the bead toe portion 4T is set in a range of 18 to 20 mm and wider than the bead base width W4 of the conventional off-road tire. In the conventional off-road tire, the core width W5 is about 6 to 7 mm, and the bead base width W4 is about 14 to 17.5 mm.

  In the pneumatic tire, when a tension is applied to the carcass cord, a rotational moment around the bead core center point acts on the bead portion 4 and bead rotation deformation occurs in a direction in which the bead toe portion 4T is lifted. On the other hand, in the tire 1 of the present embodiment, the core width W5 and the bead base width W4 are set wide, so that the resistance against the bead rotation deformation can be increased. Furthermore, in the tire 1 of the present embodiment, aramid fibers are used for the bead flipper 10. Since this aramid fiber has a very large tensile elastic modulus, the bead core 5 and the bead apex rubber 8 can be more firmly integrated, and the bead apex rubber 8 becomes a large resistance and has a resistance to bead rotation deformation. It can be further increased. As a result, when cornering on a hard road surface, tire deformation in which a portion from the bead portion 4 to the sidewall portion 3 falls to the outside in the tire axial direction is suppressed, and steering stability can be improved.

  In addition, since the increase in the longitudinal spring constant of the tire can be suppressed to a low level, road surface followability with respect to the uneven road surface can be secured, and the traction on the uneven road surface can be maintained at a high level.

  Furthermore, in the tire 1 of the present embodiment, the stability of the seating with the rim is increased by increasing the core width W5 and the bead base width W4 and suppressing the bead rotation deformation. Therefore, it is possible to improve the anti-rim removal performance without increasing the fitting pressure with the rim, that is, without impairing the rim assembly performance.

  If the core width W5 is less than 8 mm, the bead base width W4 is less than 18 mm, and the aramid fiber is not used for the bead flipper 10, the effect of suppressing the bead rotation deformation is too small, and the steering stability on the hard road surface is reduced. It cannot be improved sufficiently. In the bead core 5, the total number of turns of the bead wire is limited in order to suppress an unnecessary increase in the core weight. Therefore, when the core width W5 exceeds 10 mm, the core height decreases and the bead core 5 decreases. As a result, the bead core 5 itself is easily deformed, and the fitting force with the rim is reduced to reduce the steering stability, and the effect of suppressing the bead rotation deformation is not sufficiently exhibited. If the core width W5 is set to be larger than 10 mm by increasing the total number of turns, the bead core 5 is increased in size, causing an unnecessary increase in tire weight and adversely affecting the rim assembly performance. Also, when the bead base width W4 exceeds 20 mm, the bead portion 4 becomes large, causing an unnecessary increase in tire weight and adversely affecting the rim assembly performance.

  The core peripheral rubber layer 11 provided in the bead portion 4 is made of hard rubber and can harden the periphery of the bead core 5 to restrain the movement of the bead core 5 itself around the core center point. Therefore, the bead rotation deformation can be further suppressed, and the effect of improving the steering stability on a hard road surface can be further enhanced.

  Further, the toe reinforcing rubber 14 can also suppress the expansion deformation when the bead toe portion 4T is lifted from the rim by being made of hard rubber, and can further suppress the bead rotation deformation by suppressing the lift of the bead toe portion 4T from the rim.

  If the rubber hardness of the core surrounding rubber layer 11 and the toe reinforcing rubber 14 is less than 70 °, respectively, the effect of suppressing the bead rotation deformation becomes insufficient. On the other hand, if it exceeds 80 °, it becomes too hard and adversely affects the rim assembly performance, and may cause damage such as cracking. Even when the thicknesses t11 and t14 of the core surrounding rubber layer 11 and the toe reinforcing rubber 14 are less than 0.2 mm, the effect of suppressing the bead rotation deformation is insufficient, and when the thickness exceeds 1.0 mm. The rim assembly performance will be adversely affected.

  Next, as is well known, the belt layer 7 includes two or more belt plies 7a, 7b including two belt cords arranged at an angle of, for example, 10 to 45 ° with respect to the tire equatorial plane Co. Formed from. This belt layer 7 has a belt cord that crosses between plies to increase belt rigidity, and substantially reinforces substantially the entire width of the tread portion 2 with a tagging effect. As the belt cord, a steel cord is used in this example, but a high modulus organic fiber cord such as polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polyamide, or the like can be used as necessary.

  Further, as shown in FIG. 1, the tire 1 is formed with a cut protector 21 to prevent the sidewall portion 3 from being damaged due to contact with crushed stones, rubble, vegetation, etc. when traveling on a dirt course. Is done. The cut protector 21 has a rib shape that protrudes from the outer surface 3S of the sidewall portion 3 and extends continuously in the tire circumferential direction. The raised height h of the cut protector 21 from the outer surface 3S can be suitably in the range of 2 to 6 mm, as in the conventional off-road tire.

  The off-road pneumatic tire 1 of the present invention can be formed by removing one or both of the core peripheral rubber layer 11 and the toe reinforcing rubber 14. In addition, the carcass 6 can be formed by three carcass plies. In such a case, a so-called 3-0 structure in which the three carcass plies are folded around the bead core 5 can be adopted. A so-called 2-1 structure may be employed in which the third carcass ply is an outer ply that is rolled down from the outside in the radial direction so as to cover the folded portion of the second carcass ply 6b.

  As mentioned above, although especially preferable embodiment of this invention was explained in full detail, this invention is not limited to embodiment of illustration, It can deform | transform and implement in a various aspect.

  An off-road pneumatic tire (tire size 205 / 65R15) having the tire configuration shown in FIG. 1 was prototyped based on the specifications shown in Table 1. The test tires were mounted on a domestic four-wheel drive vehicle (2000 cc), a time trial was performed on a dirt trial course (about 1.5 km per round), and the best time of two runs each was compared. Further, during the time trial, the cornering property on the hard road surface and the traction property on the uneven road surface were evaluated by a five-point method using Comparative Example 7 as three points by driver's sensory evaluation. The higher the number, the better.

  For each test tire (internal pressure 200 kPa) mounted on the rim, a lateral force was applied from the outside of the bead portion, and the value of the lateral force when the bead portion was detached from the rim seat surface was measured as a rim detachment drag. The larger the value, the harder it is to remove the rim.

Each tire has substantially the same specifications except those listed in Table 1,
The total number of bead core bead windings is 24;
The bead apex rubber has a rubber hardness of 80 °;
The bead flipper is an organic fiber canvas cloth (thickness of warp and weft is 1670 dtex);
It was.

  As shown in Table 1, it can be confirmed that the example is excellent in cornering property on a hard road surface and traction property on an uneven road surface, and can shorten the lap time. It can also be confirmed that the rim detachability can be improved while suppressing an increase in fitting pressure.

2 Tread portion 3 Side wall portion 4 Bead portion 4T Bead toe portion 5 Bead core 6 Carcass 6A Main body portion 6B Folded portion 8 Bead apex rubber 10 Bead flipper 10a Flipper bottom portion 10i Flipper inner portion 10o Flipper outer portion 11 Core surrounding rubber layer 11a Base portion 11i Inner rising portion 11o Outside rising portion 12 Chafer 12a Chafer bottom piece 12i Chafer inner piece 12o Chafer outer piece 13 L-shaped main portion 13a Bottom portion 13b Inner portion 14 Toe reinforcement rubber W4 Bead base width W5 Core width

Claims (4)

There are a main body part that extends from the tread part through the sidewall part to the bead core of the bead part, and two or more folded parts that fold around the bead core from both ends of the main body part outward from the inner side in the tire axial direction. Carcass consisting of carcass plies,
A bead apex rubber that extends from the bead core to the outside in the radial direction through the space between the body portion and the folded portion;
And at both ends in the tire axial direction of the bottom of the flipper that is in contact with the inner surface in the radial direction of the bead core, the inner portion of the flipper that is cut off in contact with the inner side surface in the tire axial direction of the bead apex rubber, and the outer side in the tire axial direction of the bead apex rubber is cut off. A bead flipper made of a rubberized woven fabric of organic fibers and a U-shaped bent outer side of the flipper,
A core width in the tire axial direction of the bead core is 8 to 10 mm,
And the bead base width in the tire axial direction from the tire axial direction outer side surface of the bead portion to the tip of the bead toe portion is 18 to 20 mm,
Moreover, an off-road pneumatic tire using aramid fibers as the organic fibers of the bead flipper.   The bead portion includes a base portion along the flipper bottom portion, an inner rising portion along the flipper inner portion, and an outer rising portion along the flipper outer portion between the carcass and the bead flipper. The off-road according to claim 1, further comprising a core-periphery rubber layer made of a hard rubber having a U-shape and having a thickness of 0.2 to 1.0 mm and a rubber hardness of 70 to 80 °. Pneumatic tires.   The bead portion has a U-shape including a chafer bottom piece portion forming a radially inner surface of the bead portion, a chafer inner piece portion forming an inner surface of the bead portion, and a chafer outer piece portion forming an outer surface of the bead portion. An L-shape having a sheet-shaped chafer for preventing rim displacement, and connecting a bottom portion extending along the chafer bottom piece and an inner portion extending along the chafer inner piece between the chafer and the carcass 3. A pneumatic tire for off-road use according to claim 1 or 2, wherein a toe-reinforced rubber made of hard rubber having at least a main part and having a rubber hardness of 70 to 80 ° is provided.   The pneumatic tire for off-road according to any one of claims 1 to 3, wherein the carcass includes three carcass plies.

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